Positive resist composition and patterning process

Abstract

A positive resist composition comprises a polymer comprising recurring units having a sulfonium salt incorporated therein as a base resin which becomes soluble in alkaline developer under the action of acid. The polymer generates a strong sulfonic acid upon exposure to high-energy radiation so as to facilitate effective scission of acid labile groups in the resist composition.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-031322 filed in Japan on Feb. 13, 2008, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD[0002]This invention relates to (1) a positive resist composition comprising a polymer comprising recurring units containing a sulfonium salt, and (2) a patterning process using the resist composition.BACKGROUND ART[0003]While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, DUV and VUV lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using an ArF excimer laser as the light source is thought requisite to the micropatterning technique capable of achieving a feature size of 0.13 μm or less.[0004]The ArF lithography started partial use fro...

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Benefits of technology

[0026]It is noted that the resist composition of the invention can be applied to the immersion lithography. The immersion lithography involves prebaking a resist film and exposing the resist film to light through a projection lens with a liquid medium interposed between the resist film and the projection lens. The ArF immersion lithography generally uses deionized water as the immersion medium. This technology, combined with a projection lens having a numerical aperture of at least 1.0, is important for the ArF lithography to survive to the 65 nm node and forth, with a further development thereof being accelerated.

[0027]The resist composition of the invention allows the feature size of the pattern after development to be reduced by various shrinkage techniques. For example, the hole size can be shrunk by such known techniques as thermal flow, RELACS, SAFIRE, and WASOOM. More effective shrinkage of hole size by thermal flow is possible particularly when the inventive polymer is blended with a hydrogenated cycloolefin ring-opening metathesis polymer (ROMP) having a low Tg.

[0028]The positive resist composition of the invention has many advantages. Since the base resin in the resist compositi

Problems solved by technology

Although lithography using F2 laser (157 nm) was initially thought promising as the next lithography for 45-nm node devices, its development was retarded by several problems.

However, the use of these photoacid generators in chemically amplified resist compositions for ArF lithography results in an insufficient acid strength to scissor acid labile groups on the resin, a failure of resolution or a low sensitivity.

Thus these photoacid generators are not suited for the fabrication of microelectronic devices.

Among these, perfluorooctanesulfonic acid derivatives (collectively referred to as PFOS) are considered problematic with respect to their non-degradability and biological lo concentration in the environment.

However, even when these acid generators are used, the line edge roughness (LER) of a resist pattern is still a problem.

It is pointed out that with a progress of miniaturization, the edge roughness of a photoresist after development is reflected by the edge roughness after etching, which is detrimental to device characteristics.

The increased amount of acid generator, however, reduces transparency so that the resist profile is tapered or increases the aci

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